We have determined simultaneously the ADAp and Lp/Ls ratio in 138 pleural effusions: 61 tuberculous; 42 malignant; 14 transudates; five parapneumonic uncomplicated; six empyematous; and ten cases belonging to a miscellaneous group which included two disseminated lupus erythematosus; two posttraumatic; one pancreatitis; one pleuropericarditis by Mycoplasma; one viral pleuropericarditis; and three pulmonary embolisms. This has allowed us to clear the overlapping for the ADAp activity among tuberculous patients (two cases of lupus and three cases of malignant effusions) in our series. The overlap in the Lp/Ls ratio among tuberculous patients, two malignant, and two parapneumonic uncomplicated cases was also cleared. Fixing the ADAp values at 33 U and the Lp/Ls ratio at 1.2, the tuberculous pleural effusion cases were differentiated from the nontuberculous with a sensibility, positive predictive value, negative predictive value, and safety diagnosis of 100 percent. It has been proven that there is a good correlation between ADAp and Lp/Ls ratio (r = 0.717) and the ADAp and Lp (r = 0.660).